THe long-term goal of these studies is to add to our basic knowledge of the mechanism of gene regulation. There are three objectives: 1. We should like to know whether the order of replication of individual genes can be observed on a molecular level and whether different cell types of the same organism exhibit different patterns in the temporal order of DNA replication. The time of replication of the globin gene will be determined. Density-labeling with BUdR will be used to isolate DNA replicated during selected time intervals of the DNA synthetic period. The number of globin genes replicated will be determined by Cot analysis using as a probe radioactive DNA complementary to globin mRNA. These replication times will be compared in an erythroid cell and in a cell that has differentiated along a different pathway. 2. Purified SV40 virus will be used to induce host DNA synthesis in contact inhibited monkey cells. We will determine the effect on the temporal order of host DNA replication due to different host DNA sequences present in preparations of this DNA tumor virus containing defective virus genomes. 3. Investigations of the DNA of normal and malignant cells will be continued. Studies on the organization of DNA in mammalian metaphase chromosomes will be carried out to distinguish among several possible models. Chromosome fractionation procedures will be developed further to make possible the isolation of the human X chromosome and the Philadelphia chromosome associated with chronic granulocytic leukemia. Isolated metaphase chromosomes will also be used to gain information about the mechanism of DNA mediate transformation of mammalian cells. Studies will be carried out concerning the possible site of integration of the donor DNA on the genome of the recipient cell and on the frequency of co-transfer of linked markers.